- Email: [email protected]
In-process measurement of topography change of grinding wheel by using hydrodynamic pressure
International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
In-process measurement of topography change of grinding wheel by using hydrodynamic pressure Katsushi Furutani a,∗, Noriyuki Ohguro b, Nguyen Trong Hieu a, Takashi Nakamura c a
Toyota Technological Institute, 12-1, Hisakata 2-chome, Tempaku-ku, Nagoya 468-8511 Japan b Toyota Technological Institute (Daikin Industries, Ltd. at present), Japan c Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 Japan Received 3 January 2002; accepted 11 June 2002
Abstract This paper deals with an in-process measurement method for topography change of a grinding wheel, which can apply to wet grinding. A pressure sensor is set beside a grinding wheel with a small gap. When grinding fluid is dragged into the gap, hydrodynamic pressure, which corresponds to the gap length and the topography, can be measured. This method is applied to a cylindrical grinding machine. No electromagnetic properties of a workpiece and a grinding wheel affect measured results. The pressure is decreased with the increase of the gap length when the grinding fluid is supplied in the tangential direction of the grinding wheel. Spectra of the pressure are measured with an FFT analyzer. Higher frequency components are increased with the progress of grinding because of turbulent flow. Loading and dulling of a grinding wheel can be detected by the proposed method as well as its wear. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Grinding wheel; Loading; Dulling; Frequency analysis
1. Introduction Wet grinding is one of the major ways of high-precision machining. An error factor in grinding is wear of a grinding wheel. In order to reduce machining error, inprocess measurement of the grinding wheel wear is required. Loading, dulling and shedding on a grinding wheel frequently occur under inappropriate grinding conditions. Eventually, the surface of a workpiece is burned. The working surface of a grinding wheel is dressed at a certain interval to avoid the burning. Therefore, it is very important to measure both wear amount and topography change of a grinding wheel during grinding process. Grinding fluid, which causes the difficulty of the inprocess measurement, is often used to cool a workpiece. Some in-process measurement methods of wear of a
Corresponding author. Tel.: +81-52-809-1796; fax: +81-52-8097121. E-mail address: [email protected] (K. Furutani). ∗
grinding wheel have been proposed for dry and wet grinding [1–3]. Some noncontact methods to detect or measure loading, dulling and shedding of a grinding wheel have also been proposed by using a triangulation displacement sensor [4], a laser co-focusing sensor with a knife edge [5] or a CCD camera [6] for dry grinding. Because the grinding fluid disturbs light, it must be removed by these methods. Though the contact method with a wire can be used in both dry and wet grinding [7], the wire diameter restricts the resolution of detectable. Sensing acoustics [8] or vibration [9] has been also proposed for both dry and wet grinding. However, they are indirect methods. Some measurement methods, by measuring static pressure caused by issuing fluid to a grinding wheel, have been proposed [10–12]. Because these methods are similar to an air micrometer, superfluous grinding fluid must be removed for accurate measurement. The authors have proposed a measurement method by using hydrodynamic pressure [13–14]. This method actively uses the grinding fluid to generate the pressure. The topography of the working surface of a grinding wheel affects the flow of the grinding fluid. Therefore,
0890-6955/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 0 - 6 9 5 5 ( 0 2 ) 0 0 0 7 3 - 1
1448
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
it is expected that the topography change can be measured by analyzing the pressure. In this paper, the in-process measurement method of a grinding wheel in wet condition is introduced. Then the relationship between the topography and the pressure during grinding is discussed.
2. Principle of measurement Fig. 1 shows the measurement principle in the case of applying to a surface grinding process [13,14]. A pressure sensor is set beside a grinding wheel. Additional grinding fluid is poured near the gap between the grinding wheel and a pressure sensor. Grinding fluid is dragged by the rotation of the grinding wheel into the gap. Hydrodynamic pressure is generated in the gap, then the pressure change caused by the hydrodynamic pressure is measured with the sensor. The hydrodynamic pressure decreases with the increase of the gap length between the sensor and the surface of grinding wheel. After a relationship between the gap and the pressure is calibrated, the gap can be measured by measuring the pressure. The electromagnetic properties of the grinding wheel, a workpiece and grinding fluid do not affect the pressure. Viscosity of the grinding fluid seldom changes during grinding even if the temperature of the working fluid is slightly changed or debris is mixed. The diameter change by the wear seldom affects the peripheral speed of the grinding wheel because the ratio of the wear to the diameter is very small. Therefore, the measurement process by this method becomes easier and more accurate than the measurement process with other noncontact
sensors. Because the grinding fluid is actively used, no other additional device is needed. A roughness of the working surface of a grinding wheel changes because of loading, dulling and shedding during grinding, and affects flow in the gap. As a surface becomes rougher, flow is separated earlier in general and becomes more turbulent. It is expected that its frequency components change. The influence of the roughness is investigated by frequency analysis.
3. Experimental setup An external cylindrical grinding machine is used in the following experiments. Table 1 shows specifications of the grinding machine and a grinding wheel. The grinding wheel is composed of grains made from white fused alumina with an average diameter of 250 µm. This is generally used to grind steel. Fig. 2 shows an arrangement of a pressure sensor. The sensor is covered with a plate with a hole of 1 mm to avoid the direct contact with the grinding wheel. The surface roughness of the plate is 1.7 µmRz. Table 2 shows specifications of the pressure sensor. The sensor with diaphragm of 6 mm in diameter is a strain gauge type. The sensitivity of the pressure sensor is 10 kPa/V at the output of a strain amplifier. The sensor unit is mounted on the table of the grinding machine with a combination of an xyz and a rotational stages, which can be mounted and dismounted with a magnet chuck. The pressure becomes maximum at 5 mm above the contact point of the grinding wheel with a workpiece. The sensor unit is removed during grinding. The pressure sensor must exactly be put back after the grinding process by adjusting the position with the stage. The gap is measured with an eddy current displacement sensor with a measurement range of 1 mm and a resolution of 0.4 µm. Soluble-type grinding fluid containing surfactant is diluted 70 times with water. The grinding fluid is supplied at the maximum flow rate of 1.3×10⫺4 m3/s through a regulator.
4. Experiment 4.1. Adjustment of gap length
Fig. 1. Measurement principle by using pressure.
The gap length between the grinding wheel and the plate mounting the sensor must be adjusted before the experiments. Fig. 3 shows the adjustment process of the gap length. The sensor is arranged parallel to the working surface of the grinding wheel. When the grinding wheel contacts with the plate detecting by a spark on the plate, this length of the gap is defined as zero. Then, the spindle
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
1449
Table 1 Specifications of grinding machine Cylindrical grinding machine Grinding wheel
Revolution of grinding wheel Maximum peripheral speed Type Grain Average grain size Bond Diameter Width
26.8 s⫺1 29.9 m/s JIS-WA60J7V White fused alumina 250 µm Vitrified 355 mm 50 mm
Fig. 4 shows two arrangements of a nozzle. The grinding fluid is supplied from the 20° and tangential directions, respectively. Fig. 5 shows a relationship between the pressure and the flow rate. The pressure sensitively changes below a flow rate of 6×10⫺5 m3/s with the inclined nozzle. The grinding fluid is frothed with the rough surface of the grinding wheel. This trend grows as the flow rate is increased with the inclined nozzle. However, the pressure is almost flat with the tangential nozzle. The supply from the tangential direction makes the pressure robuster against the ripple of the grinding fluid. The grinding fluid is supplied from the tangential direction in the following experiments.
4.3. Relationship between pressure and gap length
Fig. 2.
Arrangement of pressure sensor.
is moved backward to change the gap. Its change is measured by measuring the displacement of the spindle with the displacement sensor. The removed depth on the plate in the zero detection procedure is measured with a surface roughness tester to compensate the gap length after the experiments. 4.2. Influence of supplying direction of grinding fluid for measurement A flow rate of the grinding fluid and a nozzle position affect conditions in the gap [15]. Their influence on the pressure is investigated.
A trend that the pressure is decreased with the increase of the gap is obtained [13,14]. The relationship between the pressure and the gap length must be calibrated for each grinding wheel before actual measurement. Fig. 6 shows a relationship between the pressure and the gap length in the case of using the grinding wheel shown in Table 2. The spindle is moved to change the gap. The grinding fluid is supplied at a flow rate of 4.2×10⫺5 m3/s. The peripheral speed of the grinding wheel is set to 26 m/s. The pressure is linearly decreased with a sensitivity of 150 Pa/µm from 5 to 30 µm under the conditions shown in Table 2. The pressure changes in the same way in both the cases of changing the diameter of the grinding wheel by dressing and of adjusting the spindle position because the diameter change affects its peripheral speed little.
Table 2 Specifications of pressure sensor Pressure sensor
Strain amplifier
Type Nominal pressure Diameter of diaphragm Natural frequency Linearity Band width Accuracy Linearity
Strain gauge (diaphragm) 100 kPa 6 mm 22 kHz 1% DC-200 kHz ±0.1% of full scale ±0.01% of full scale
1450
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
Fig. 3.
Gap adjustment process. (a) Setting zero-gap length. (b) Measurement of gap length.
Fig. 4. Arrangement of nozzle. (a) 20°-direction. (b) Tangential direction.
4.4. Pressure change caused by loading Table 3 shows grinding conditions to accelerate loading of the working surface. Mild material, aluminum, is used for a workpiece. Against the general grinding conditions, the structure of the grinding wheel is porous and the peripheral speed of the workpiece is slow to deposit debris on the grinding wheel by the accumulated heat. Total amount of grinding was 208 mm2 after grinding to a thickness of 50 µm. The wear of the grinding wheel is too small to measure it. Frequency components are observed with a Fast Fourier Transform (FFT) analyzer. Fig. 7 shows an example of spectra of the pressure,
Fig. 5. Relationship between pressure and flow rate. (a) 20°-direction. (b) Tangential direction.
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
Fig. 6.
Relationship between pressure and gap length.
Fig. 7.
higher flow rate. The grain size and porousness of the bond affect the increasing frequency components in the progress of grinding. Fig. 8 shows a change of the spectra of the pressure with a progress of grinding. Horizontal lines indicate 0.1 kPa in each set of spectra. Table 4 shows grinding conditions. Bearing steel (JIS-SUJ2, ASTM-52100) is ground to a thickness of 10 µm to remove cracked part of grains just after dressing. Then the pressure is observed during grinding aluminum. Though the spectra from 400 to 500 Hz is observed very little after dressing and the initial wear by grinding bearing steel, they are increased with a progress of grinding. This bandwidth depends on the structure of the grinding wheel. Fig. 9 shows a dependency of frequency components of the pressure on the gap length. Higher components decrease with the increase of the gap length. A smaller gap is preferable to detect the topography change.
Example of spectra of pressure.
which is the average of 50 measurements to avoid random errors. The initial gap is set to 20 µm. As the gap between the sensor and the grinding wheel increases with the progress of grinding, total pressure becomes smaller. However, some components, mainly a frequency of 350 Hz in this case, are increased after grinding. The roughness of the working surface of the grinding wheel is decreased from 285 to 191 µmRz and from 13 to 9 µmRa because of the loading. No diameter change is measured. This trend is clearly observed at a
Fig. 8.
Change of spectra of pressure with progress of loading.
Table 3 Grinding conditions to accelerate loading Grinding wheel Dressing conditions Grinding conditions Workpiece
1451
Type Peripheral speed Depth of dressing Feed speed Method Depth of grinding Material Peripheral speed Rotational direction
WA60J7V 26 m/s 10 µm 5 µm/s Plunge grinding 2.5 µm Aluminum (JIS-A2014, ASTM-2014), φ30 mm 0.13 m/s Reverse of grinding wheel
1452
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
Table 4 Experimental conditions for progress of loading Grinding wheel
Grinding wheel Peripheral speed Depth of dressing Feed of table Workpiece Peripheral speed Depth of grinding Amount Workpiece Peripheral speed Depth of grinding Amount Initial gap Flow rate
Dressing conditions Initial wear
Loading
Pressure measurement
WA60J7V 26 m/s 10 µm 5.2 mm/s Bearing steel (JIS-SUJ2, ASTM-52100) 0.27 m/s 2.5 µm 40 mm2 Aluminum (JIS-A2014, ASTM-2014), φ30 mm 0.13 m/s 2.5 µm 14 mm2 10 µm 8.3×10⫺5m3/s
Table 5 Grinding conditions for measurement of dulling Grinding wheel Dressing conditions Grinding conditions
Grinding wheel Peripheral speed Depth of dressing Feed of table Method Workpiece Peripheral speed Depth of grinding
WA60J7V 26 m/s 10 µm 5.2 mm/s Plunge grinding Tungsten carbide φ40 mm 0.33 m/s less than 1 µm
Fig. 10 shows examples of the spectra of the pressure before and after dulling. The spectra in a higher frequency range are increased as well as loading. Therefore, dulling can be detected by this method. The discrimination among loading, dulling and shedding should be considered for detail analysis of the topography of the grinding wheel. However, it is enough to detect the necessity of dressing.
Fig. 9.
Comparison of spectra with respect to gap length.
4.5. Pressure change caused by dulling The working surface becomes flat also by dulling. Inprocess measurement of dulling is also tried. After grinding a tungsten carbide rod with a diameter of 40 mm to a thickness of 50 µm with a depth of cut less than 1 µm, the working surface of the grinding wheel is dulled.
Fig. 10.
Example of pressure spectra before and after dulling.
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
5. Conclusions In this paper, the topography change of a grinding wheel is observed by using hydrodynamic pressure. The conclusions can be drawn as follows.
[4] [5]
1. Spectra of the pressure in higher frequency are increased with the progress of loading and dulling. 2. Not only the flow rate but also turbulent flow of the grinding fluid and air affect the measured pressure. Consequently, the topography change can be measured by using the pressure. 3. The pressure is decreased with the increase of the gap length in case of a narrow gap. The diameter of a grinding wheel measured by this method changes by the wear and topography caused by loading, dulling and shedding. Their influence should be discriminated in the measurement process in future.
[6]
[7]
[8]
[9]
Acknowledgements The authors wish to thank Mr. Masaru Ohta and Mr. Susumu Kozakai of Toyota Technological Institute for their helpful cooperation. This study is financially supported by Osawa Scientific Grant (OSG Fund), Fluid Power Technology Foundation, and Grant-in-Aid for High-tech Research Center ‘Space Robotics Research Center’ and for Academic Frontier Center ‘Future Data Storage Materials’ by the Ministry of Education, Culture, Sports, Science and Technology, Japan.
[10]
[11]
[12]
[13]
References [14] [1] W.P. Dong, L. Annecchino, J.A. Webster, On-line measurement of grinding wheel wear using acoustic emission, in: Proc. 11th Annual Meeting of American Society for Precision Engineering, Monterey, CA, Nov. 1996, 1996, pp. 566–571. [2] G. Spur, F. Leonards, Sensoren zur Erfassung von Prozesskenngro¨ ssen bei der Drehbearbeitung, Annals of the CIRP 24 (1) (1975) 349–355 (in German). [3] M. Izumi, H.S. Lee, T. Wakabayashi, S. Inoue, Development of
[15]
1453
a measuring instrument for grinding wheel peripheral shapes, in: Proceedings of 15th Annual Meeting of American Society for Precision Engineering, Scottsdale, AZ, Oct. 2000, 2000, pp. 377–380. E. Brinksmeier, F. Werner, Monitoring of grinding wheel wear, Annals of the CIRP 41 (1) (1992) 373–376. Y. Kakino, A. Matsubara, J. Yamaji, In-situ measurement of grinding wheel surface topography (1st Report) development of measuring system using laser stylus, International Journal of Japan Society for Precision Engineering 31 (4) (1997) 273–277. H. Yasui, Y. Hiraki, M. Sakata, Development of automatic image processing system for evaluation of wheel surface condition in ultra-smoothness grinding, in: Proceedings of 16th Annual Meeting of American Society for Precision Engineering, Arlington, VA, Nov. 2001, 2001, pp. 62–65. M. Izumi, H.S. Lee, S. Inoue, Study on a measuring method for grain cutting edges in grinding wheel surface, in: Proceedings of 16th Annual Meeting of American Society for Precision Engineering, Arlington, VA, Nov. 2001, 2001, pp. 417–420. S. Hagiwara, T. Obikawa, M. Gomi, T. Matsumura, T. Iizuna, A. Yui, Prediction of grinding status based on dressing sounds— approaches by linear prediction method and neural network, Journal of Japan Society for Precision Engineering 67 (1) (2001) 137– 141 (in Japanese). A. Hosokawa, K. Sakuma, T. Ueda, In situ characterization of grinding wheel surface, in: Proceedings of 14th Annual Meeting of American Society for Precision Engineering, Monterey, CA, Nov. 1999, 1999, pp. 99–102. H.J. Schreitmu¨ ller, M. Dederichs, Pneumatisches Meßverfahren zur Ermittlung des Schleif-scheibenverschleißes, IndustrieAnzeiger 93 (68) (1971) 1733–1734 (in German). T.M.A. Maksoud, A.A. Mokbel, J.E. Morgan, In-process detection of grinding wheel truing and dressing conditions using a flapper nozzle arrangement, Proceedings of Institution of Mechanical Engineers, Journal of Engineering Manufacturing 211 (B(5)) (1997) 335–343. J.F. Rahman, V. Radhakrishnan, Measurement of grinding wheel surface topography using electra-pneumatic turbulence amplifier system, International Journal of Machine Tool Design and Research 20 (3-4) (1980) 189–196. K. Furutani, T. Katoh, N. Mohri, In-process measurement of wear of grinding wheel by using hydrodynamic pressure in wet grinding condition (1st Report)—measurement principle, Journal of Japan Society for Precision Engineering 66 (1) (2000) 127–131 (in Japanese). K. Furutani, T. Katoh, N. Mohri, In-process measurement of wear of grinding wheel by hydrodynamic pressure, in: Proceedings of 14th Annual Meeting of American Society for Precision Engineering, Monterey, California, USA, Nov. 1999, 1999, pp. 610– 613. S. Ebbrell, N.H. Woolley, Y.D. Tridimas, D.R. Allanson, W.B. Rowe, The effects of cutting fluid application methods on the grinding process, International Journal of Machine Tools and Manufacturing 40 (2) (2000) 209–223.
In-process measurement of topography change of grinding wheel by using hydrodynamic pressure Katsushi Furutani a,∗, Noriyuki Ohguro b, Nguyen Trong Hieu a, Takashi Nakamura c a
Toyota Technological Institute, 12-1, Hisakata 2-chome, Tempaku-ku, Nagoya 468-8511 Japan b Toyota Technological Institute (Daikin Industries, Ltd. at present), Japan c Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 Japan Received 3 January 2002; accepted 11 June 2002
Abstract This paper deals with an in-process measurement method for topography change of a grinding wheel, which can apply to wet grinding. A pressure sensor is set beside a grinding wheel with a small gap. When grinding fluid is dragged into the gap, hydrodynamic pressure, which corresponds to the gap length and the topography, can be measured. This method is applied to a cylindrical grinding machine. No electromagnetic properties of a workpiece and a grinding wheel affect measured results. The pressure is decreased with the increase of the gap length when the grinding fluid is supplied in the tangential direction of the grinding wheel. Spectra of the pressure are measured with an FFT analyzer. Higher frequency components are increased with the progress of grinding because of turbulent flow. Loading and dulling of a grinding wheel can be detected by the proposed method as well as its wear. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Grinding wheel; Loading; Dulling; Frequency analysis
1. Introduction Wet grinding is one of the major ways of high-precision machining. An error factor in grinding is wear of a grinding wheel. In order to reduce machining error, inprocess measurement of the grinding wheel wear is required. Loading, dulling and shedding on a grinding wheel frequently occur under inappropriate grinding conditions. Eventually, the surface of a workpiece is burned. The working surface of a grinding wheel is dressed at a certain interval to avoid the burning. Therefore, it is very important to measure both wear amount and topography change of a grinding wheel during grinding process. Grinding fluid, which causes the difficulty of the inprocess measurement, is often used to cool a workpiece. Some in-process measurement methods of wear of a
Corresponding author. Tel.: +81-52-809-1796; fax: +81-52-8097121. E-mail address: [email protected] (K. Furutani). ∗
grinding wheel have been proposed for dry and wet grinding [1–3]. Some noncontact methods to detect or measure loading, dulling and shedding of a grinding wheel have also been proposed by using a triangulation displacement sensor [4], a laser co-focusing sensor with a knife edge [5] or a CCD camera [6] for dry grinding. Because the grinding fluid disturbs light, it must be removed by these methods. Though the contact method with a wire can be used in both dry and wet grinding [7], the wire diameter restricts the resolution of detectable. Sensing acoustics [8] or vibration [9] has been also proposed for both dry and wet grinding. However, they are indirect methods. Some measurement methods, by measuring static pressure caused by issuing fluid to a grinding wheel, have been proposed [10–12]. Because these methods are similar to an air micrometer, superfluous grinding fluid must be removed for accurate measurement. The authors have proposed a measurement method by using hydrodynamic pressure [13–14]. This method actively uses the grinding fluid to generate the pressure. The topography of the working surface of a grinding wheel affects the flow of the grinding fluid. Therefore,
0890-6955/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 0 - 6 9 5 5 ( 0 2 ) 0 0 0 7 3 - 1
1448
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
it is expected that the topography change can be measured by analyzing the pressure. In this paper, the in-process measurement method of a grinding wheel in wet condition is introduced. Then the relationship between the topography and the pressure during grinding is discussed.
2. Principle of measurement Fig. 1 shows the measurement principle in the case of applying to a surface grinding process [13,14]. A pressure sensor is set beside a grinding wheel. Additional grinding fluid is poured near the gap between the grinding wheel and a pressure sensor. Grinding fluid is dragged by the rotation of the grinding wheel into the gap. Hydrodynamic pressure is generated in the gap, then the pressure change caused by the hydrodynamic pressure is measured with the sensor. The hydrodynamic pressure decreases with the increase of the gap length between the sensor and the surface of grinding wheel. After a relationship between the gap and the pressure is calibrated, the gap can be measured by measuring the pressure. The electromagnetic properties of the grinding wheel, a workpiece and grinding fluid do not affect the pressure. Viscosity of the grinding fluid seldom changes during grinding even if the temperature of the working fluid is slightly changed or debris is mixed. The diameter change by the wear seldom affects the peripheral speed of the grinding wheel because the ratio of the wear to the diameter is very small. Therefore, the measurement process by this method becomes easier and more accurate than the measurement process with other noncontact
sensors. Because the grinding fluid is actively used, no other additional device is needed. A roughness of the working surface of a grinding wheel changes because of loading, dulling and shedding during grinding, and affects flow in the gap. As a surface becomes rougher, flow is separated earlier in general and becomes more turbulent. It is expected that its frequency components change. The influence of the roughness is investigated by frequency analysis.
3. Experimental setup An external cylindrical grinding machine is used in the following experiments. Table 1 shows specifications of the grinding machine and a grinding wheel. The grinding wheel is composed of grains made from white fused alumina with an average diameter of 250 µm. This is generally used to grind steel. Fig. 2 shows an arrangement of a pressure sensor. The sensor is covered with a plate with a hole of 1 mm to avoid the direct contact with the grinding wheel. The surface roughness of the plate is 1.7 µmRz. Table 2 shows specifications of the pressure sensor. The sensor with diaphragm of 6 mm in diameter is a strain gauge type. The sensitivity of the pressure sensor is 10 kPa/V at the output of a strain amplifier. The sensor unit is mounted on the table of the grinding machine with a combination of an xyz and a rotational stages, which can be mounted and dismounted with a magnet chuck. The pressure becomes maximum at 5 mm above the contact point of the grinding wheel with a workpiece. The sensor unit is removed during grinding. The pressure sensor must exactly be put back after the grinding process by adjusting the position with the stage. The gap is measured with an eddy current displacement sensor with a measurement range of 1 mm and a resolution of 0.4 µm. Soluble-type grinding fluid containing surfactant is diluted 70 times with water. The grinding fluid is supplied at the maximum flow rate of 1.3×10⫺4 m3/s through a regulator.
4. Experiment 4.1. Adjustment of gap length
Fig. 1. Measurement principle by using pressure.
The gap length between the grinding wheel and the plate mounting the sensor must be adjusted before the experiments. Fig. 3 shows the adjustment process of the gap length. The sensor is arranged parallel to the working surface of the grinding wheel. When the grinding wheel contacts with the plate detecting by a spark on the plate, this length of the gap is defined as zero. Then, the spindle
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
1449
Table 1 Specifications of grinding machine Cylindrical grinding machine Grinding wheel
Revolution of grinding wheel Maximum peripheral speed Type Grain Average grain size Bond Diameter Width
26.8 s⫺1 29.9 m/s JIS-WA60J7V White fused alumina 250 µm Vitrified 355 mm 50 mm
Fig. 4 shows two arrangements of a nozzle. The grinding fluid is supplied from the 20° and tangential directions, respectively. Fig. 5 shows a relationship between the pressure and the flow rate. The pressure sensitively changes below a flow rate of 6×10⫺5 m3/s with the inclined nozzle. The grinding fluid is frothed with the rough surface of the grinding wheel. This trend grows as the flow rate is increased with the inclined nozzle. However, the pressure is almost flat with the tangential nozzle. The supply from the tangential direction makes the pressure robuster against the ripple of the grinding fluid. The grinding fluid is supplied from the tangential direction in the following experiments.
4.3. Relationship between pressure and gap length
Fig. 2.
Arrangement of pressure sensor.
is moved backward to change the gap. Its change is measured by measuring the displacement of the spindle with the displacement sensor. The removed depth on the plate in the zero detection procedure is measured with a surface roughness tester to compensate the gap length after the experiments. 4.2. Influence of supplying direction of grinding fluid for measurement A flow rate of the grinding fluid and a nozzle position affect conditions in the gap [15]. Their influence on the pressure is investigated.
A trend that the pressure is decreased with the increase of the gap is obtained [13,14]. The relationship between the pressure and the gap length must be calibrated for each grinding wheel before actual measurement. Fig. 6 shows a relationship between the pressure and the gap length in the case of using the grinding wheel shown in Table 2. The spindle is moved to change the gap. The grinding fluid is supplied at a flow rate of 4.2×10⫺5 m3/s. The peripheral speed of the grinding wheel is set to 26 m/s. The pressure is linearly decreased with a sensitivity of 150 Pa/µm from 5 to 30 µm under the conditions shown in Table 2. The pressure changes in the same way in both the cases of changing the diameter of the grinding wheel by dressing and of adjusting the spindle position because the diameter change affects its peripheral speed little.
Table 2 Specifications of pressure sensor Pressure sensor
Strain amplifier
Type Nominal pressure Diameter of diaphragm Natural frequency Linearity Band width Accuracy Linearity
Strain gauge (diaphragm) 100 kPa 6 mm 22 kHz 1% DC-200 kHz ±0.1% of full scale ±0.01% of full scale
1450
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
Fig. 3.
Gap adjustment process. (a) Setting zero-gap length. (b) Measurement of gap length.
Fig. 4. Arrangement of nozzle. (a) 20°-direction. (b) Tangential direction.
4.4. Pressure change caused by loading Table 3 shows grinding conditions to accelerate loading of the working surface. Mild material, aluminum, is used for a workpiece. Against the general grinding conditions, the structure of the grinding wheel is porous and the peripheral speed of the workpiece is slow to deposit debris on the grinding wheel by the accumulated heat. Total amount of grinding was 208 mm2 after grinding to a thickness of 50 µm. The wear of the grinding wheel is too small to measure it. Frequency components are observed with a Fast Fourier Transform (FFT) analyzer. Fig. 7 shows an example of spectra of the pressure,
Fig. 5. Relationship between pressure and flow rate. (a) 20°-direction. (b) Tangential direction.
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
Fig. 6.
Relationship between pressure and gap length.
Fig. 7.
higher flow rate. The grain size and porousness of the bond affect the increasing frequency components in the progress of grinding. Fig. 8 shows a change of the spectra of the pressure with a progress of grinding. Horizontal lines indicate 0.1 kPa in each set of spectra. Table 4 shows grinding conditions. Bearing steel (JIS-SUJ2, ASTM-52100) is ground to a thickness of 10 µm to remove cracked part of grains just after dressing. Then the pressure is observed during grinding aluminum. Though the spectra from 400 to 500 Hz is observed very little after dressing and the initial wear by grinding bearing steel, they are increased with a progress of grinding. This bandwidth depends on the structure of the grinding wheel. Fig. 9 shows a dependency of frequency components of the pressure on the gap length. Higher components decrease with the increase of the gap length. A smaller gap is preferable to detect the topography change.
Example of spectra of pressure.
which is the average of 50 measurements to avoid random errors. The initial gap is set to 20 µm. As the gap between the sensor and the grinding wheel increases with the progress of grinding, total pressure becomes smaller. However, some components, mainly a frequency of 350 Hz in this case, are increased after grinding. The roughness of the working surface of the grinding wheel is decreased from 285 to 191 µmRz and from 13 to 9 µmRa because of the loading. No diameter change is measured. This trend is clearly observed at a
Fig. 8.
Change of spectra of pressure with progress of loading.
Table 3 Grinding conditions to accelerate loading Grinding wheel Dressing conditions Grinding conditions Workpiece
1451
Type Peripheral speed Depth of dressing Feed speed Method Depth of grinding Material Peripheral speed Rotational direction
WA60J7V 26 m/s 10 µm 5 µm/s Plunge grinding 2.5 µm Aluminum (JIS-A2014, ASTM-2014), φ30 mm 0.13 m/s Reverse of grinding wheel
1452
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
Table 4 Experimental conditions for progress of loading Grinding wheel
Grinding wheel Peripheral speed Depth of dressing Feed of table Workpiece Peripheral speed Depth of grinding Amount Workpiece Peripheral speed Depth of grinding Amount Initial gap Flow rate
Dressing conditions Initial wear
Loading
Pressure measurement
WA60J7V 26 m/s 10 µm 5.2 mm/s Bearing steel (JIS-SUJ2, ASTM-52100) 0.27 m/s 2.5 µm 40 mm2 Aluminum (JIS-A2014, ASTM-2014), φ30 mm 0.13 m/s 2.5 µm 14 mm2 10 µm 8.3×10⫺5m3/s
Table 5 Grinding conditions for measurement of dulling Grinding wheel Dressing conditions Grinding conditions
Grinding wheel Peripheral speed Depth of dressing Feed of table Method Workpiece Peripheral speed Depth of grinding
WA60J7V 26 m/s 10 µm 5.2 mm/s Plunge grinding Tungsten carbide φ40 mm 0.33 m/s less than 1 µm
Fig. 10 shows examples of the spectra of the pressure before and after dulling. The spectra in a higher frequency range are increased as well as loading. Therefore, dulling can be detected by this method. The discrimination among loading, dulling and shedding should be considered for detail analysis of the topography of the grinding wheel. However, it is enough to detect the necessity of dressing.
Fig. 9.
Comparison of spectra with respect to gap length.
4.5. Pressure change caused by dulling The working surface becomes flat also by dulling. Inprocess measurement of dulling is also tried. After grinding a tungsten carbide rod with a diameter of 40 mm to a thickness of 50 µm with a depth of cut less than 1 µm, the working surface of the grinding wheel is dulled.
Fig. 10.
Example of pressure spectra before and after dulling.
K. Furutani et al. / International Journal of Machine Tools & Manufacture 42 (2002) 1447–1453
5. Conclusions In this paper, the topography change of a grinding wheel is observed by using hydrodynamic pressure. The conclusions can be drawn as follows.
[4] [5]
1. Spectra of the pressure in higher frequency are increased with the progress of loading and dulling. 2. Not only the flow rate but also turbulent flow of the grinding fluid and air affect the measured pressure. Consequently, the topography change can be measured by using the pressure. 3. The pressure is decreased with the increase of the gap length in case of a narrow gap. The diameter of a grinding wheel measured by this method changes by the wear and topography caused by loading, dulling and shedding. Their influence should be discriminated in the measurement process in future.
[6]
[7]
[8]
[9]
Acknowledgements The authors wish to thank Mr. Masaru Ohta and Mr. Susumu Kozakai of Toyota Technological Institute for their helpful cooperation. This study is financially supported by Osawa Scientific Grant (OSG Fund), Fluid Power Technology Foundation, and Grant-in-Aid for High-tech Research Center ‘Space Robotics Research Center’ and for Academic Frontier Center ‘Future Data Storage Materials’ by the Ministry of Education, Culture, Sports, Science and Technology, Japan.
[10]
[11]
[12]
[13]
References [14] [1] W.P. Dong, L. Annecchino, J.A. Webster, On-line measurement of grinding wheel wear using acoustic emission, in: Proc. 11th Annual Meeting of American Society for Precision Engineering, Monterey, CA, Nov. 1996, 1996, pp. 566–571. [2] G. Spur, F. Leonards, Sensoren zur Erfassung von Prozesskenngro¨ ssen bei der Drehbearbeitung, Annals of the CIRP 24 (1) (1975) 349–355 (in German). [3] M. Izumi, H.S. Lee, T. Wakabayashi, S. Inoue, Development of
[15]
1453
a measuring instrument for grinding wheel peripheral shapes, in: Proceedings of 15th Annual Meeting of American Society for Precision Engineering, Scottsdale, AZ, Oct. 2000, 2000, pp. 377–380. E. Brinksmeier, F. Werner, Monitoring of grinding wheel wear, Annals of the CIRP 41 (1) (1992) 373–376. Y. Kakino, A. Matsubara, J. Yamaji, In-situ measurement of grinding wheel surface topography (1st Report) development of measuring system using laser stylus, International Journal of Japan Society for Precision Engineering 31 (4) (1997) 273–277. H. Yasui, Y. Hiraki, M. Sakata, Development of automatic image processing system for evaluation of wheel surface condition in ultra-smoothness grinding, in: Proceedings of 16th Annual Meeting of American Society for Precision Engineering, Arlington, VA, Nov. 2001, 2001, pp. 62–65. M. Izumi, H.S. Lee, S. Inoue, Study on a measuring method for grain cutting edges in grinding wheel surface, in: Proceedings of 16th Annual Meeting of American Society for Precision Engineering, Arlington, VA, Nov. 2001, 2001, pp. 417–420. S. Hagiwara, T. Obikawa, M. Gomi, T. Matsumura, T. Iizuna, A. Yui, Prediction of grinding status based on dressing sounds— approaches by linear prediction method and neural network, Journal of Japan Society for Precision Engineering 67 (1) (2001) 137– 141 (in Japanese). A. Hosokawa, K. Sakuma, T. Ueda, In situ characterization of grinding wheel surface, in: Proceedings of 14th Annual Meeting of American Society for Precision Engineering, Monterey, CA, Nov. 1999, 1999, pp. 99–102. H.J. Schreitmu¨ ller, M. Dederichs, Pneumatisches Meßverfahren zur Ermittlung des Schleif-scheibenverschleißes, IndustrieAnzeiger 93 (68) (1971) 1733–1734 (in German). T.M.A. Maksoud, A.A. Mokbel, J.E. Morgan, In-process detection of grinding wheel truing and dressing conditions using a flapper nozzle arrangement, Proceedings of Institution of Mechanical Engineers, Journal of Engineering Manufacturing 211 (B(5)) (1997) 335–343. J.F. Rahman, V. Radhakrishnan, Measurement of grinding wheel surface topography using electra-pneumatic turbulence amplifier system, International Journal of Machine Tool Design and Research 20 (3-4) (1980) 189–196. K. Furutani, T. Katoh, N. Mohri, In-process measurement of wear of grinding wheel by using hydrodynamic pressure in wet grinding condition (1st Report)—measurement principle, Journal of Japan Society for Precision Engineering 66 (1) (2000) 127–131 (in Japanese). K. Furutani, T. Katoh, N. Mohri, In-process measurement of wear of grinding wheel by hydrodynamic pressure, in: Proceedings of 14th Annual Meeting of American Society for Precision Engineering, Monterey, California, USA, Nov. 1999, 1999, pp. 610– 613. S. Ebbrell, N.H. Woolley, Y.D. Tridimas, D.R. Allanson, W.B. Rowe, The effects of cutting fluid application methods on the grinding process, International Journal of Machine Tools and Manufacturing 40 (2) (2000) 209–223.